Underground pipelines are commonly used as fluid conduits for conveying utilities such as natural gas to an end user. Many existing pipelines are composed of sections of cast iron pipe connected by spigot joints, in which an end or "spigot" of one pipe section is interference-fitted into a "bell" or flared end of the next adjoining section, and the cavity between the bell and the spigot is filled with jute for a gas-tight seal.
Over time the jute tends to deteriorate, compromising the integrity of the joint seal, and must be repaired or replaced. Typically such pipelines are far too small for a person to enter, and such repairs have thus conventionally required excavation of the pipeline. This is a costly and time consuming process.
It is therefore advantageous to be able to effect repairs from inside the pipeline. For example, an apparatus capable of carrying out pipe repairs from inside the pipe is disclosed in U.S. Pat. No. 4,986,314. A working head provided with a tool holder is rotatably mounted on the front of a self-propelled trolley which can be inserted into a pipeline. A television camera allows the operator to locate damaged areas, and the tool holder can be fitted with the appropriate tool to effect repairs. The working head is rotatable circumferentially, to permit repairs on any part of the pipe wall.
Because the working head in this device is permanently mounted in a transverse orientation relative to the trolley, insertion of the device into a pipeline significantly reduces the effective cross-sectional area of the pipeline. This effect is exacerbated by the large trolley, which is provided with a blocking device that enables the trolley to support and resist the force of the working head when grinding, cutting etc. inside a pipe. Accordingly, the device of U.S. Pat. No. 4,986,314 still requires that the pipeline be shut down before repairs are undertaken. Moreover, the device will generally not fit through an existing opening in the pipeline, so the pipe must first be broken before the device can be introduced. These are significant disadvantages in the repair and maintenance of a natural gas pipeline.
The present invention provides a device for repairing pipes internally, and particularly for the sealing of spigot joints, which overcomes these and other disadvantages. The device comprises a cylindrical drill head pivotally mounted on a shackle so that it can be inserted into a pipeline and selectively pivoted from an axial orientation, for being fed along the pipeline, to a radial orientation for drilling into a pipe joint. The drill head is provided with a hydraulic foot which urges the drill bit against the interior of the pipe joint, and a sealant injection mechanism for injecting sealant into the jute. A camera transmits images of the pipe interior to the operator, who can thus locate and repair successive pipe joints without withdrawing the device from the pipeline.
The cross-sectional area occupied by the device of the present invention is minimal, particularly when the drill head is oriented axially. This allows the device to be used within a "live" natural gas pipeline, because the device is sufficiently compact so as not to interfere with the flow of gas. The provision of a hydraulic foot contained within the drill head not only eliminates the need for a bulky, trolley-like structure to oppose the force of drilling, but also provides significant precision in drilling depth. This is important in the drilling of pipe joints because the sealant must be injected directly into the cavity between the bell and the spigot, which is usually not very deep. These and other advantages will be apparent from the description of the invention which follows.